The Missa brevis K.140 (Anh. 235d = No. 5) occupies a special position in that it comes close to a pastoral mass, a type not otherwise represented in Mozart’s mass oeuvre. As in no other setting of the Ordinary, songlike, graceful melodies predominate; only the main part of the Credo and the first section of the Agnus Dei stand out with their serious, solemn mood.

New, important evidence for the work’s authenticity has come to light through the discovery of old parts that were written at a ti...